Reversible Guest Removal and Selective Guest Exchange with a Covalent Dinuclear Wheel-and-Axle Metallorganic Host Constituted by Half-Sandwich Ru(II) Wheels Connected by a Linear Diphosphine Axle

The organometallic unit {[(p-cymene)­RuCl2]2­[4,4′-bis­(diphenylphosphino)­biphenylene]}
has been revealed to be a good building block for the construction
of wheel-and-axle (waa) crystalline scaffolds able to incorporate
different organic solvents. In fact, the synthesis carried out in
tetrahydrofuran (THF), dichloromethane, toluene, and p-xylene led to the corresponding solvates. An apohost could instead
be isolated from diethyl ether. However, this showed a lower crystallinity
than the solvates, as usually expected for waa compounds. Thermal
extrusion of THF led to a new apohost framework. The desolvation process
occurred with partial loss of crystallinity which, however, was completely
restored after sorption of THF vapors with rebuilding of the starting
THF solvate. THF could also be exchanged with p-xylene
by a vapor uptake process, while exposure to other aromatics, such
as benzene, toluene, and o- and m-xylene led to partial guest exchanges. The use of a more branched
guest, such as p-cymene, completely blocked the exchange.
THF could be exchanged also with phenylacetylene and 4-ethynyltoluene,
although a final stable host/guest compound was isolated only with
the last. The monitoring by X-ray powder diffraction analysis of the p-xylene and phenylacetylene uptakes provided evidence that
the exchange processes occur with complete retention of crystallinity,
thus pointing out the flexibility of the crystalline networks involved
in the aforementioned dynamic processes.